1. Field of the Invention
The present invention generally relates to radio-frequency systems and, more specifically, to radiofrequency transmission (or transmission-reception) chains equipped with an impedance matching network between a transmit amplifier and an antenna.
2. Discussion of the Related Art
Radiofrequency systems, especially those used in mobile communication devices (for example, portable phones), are sensitive to disturbances linked to a change of environment (for example, the position of the user's hand with respect to the antenna). The implementation of a dynamic impedance matching network between the output of a transmit amplifier and an antenna may be provided to optimize the transmission chain. This optimization enables, among others, to optimize the power consumption of the transmit device.
To be able to control a dynamic impedance matching network, a modification in the impedance of the load connected to the output of the amplifier should be detected to be able to match the system back to a nominal value of the output impedance of this amplifier.
A directional coupler is generally used at the output of the transmit amplifier to determine the voltage standing wave ratio (VSWR). Such a coupler enables to sample part of the power transmitted over the main line for measurement purposes.
A first solution is to use an iterative algorithm to reset the impedance matching network. Such an iterative algorithm generally takes time.
To accelerate the impedance matching, it is preferred to detect the amplitude and the phase of the voltage standing wave ratio.
US-A-2006/0160501 describes an impedance matching system in which the detection of the phase and amplitude of the voltage standing Wave ratio requires two couplers on either side of the impedance matching network.
It would be desirable to have a simple and reliable system for detecting the amplitude and phase of the voltage standing wave ratio of a load of a transmit amplifier.
It would also be desirable to have a device of low bulk and cost.